The prior art of metal substrate dental technology and metal ceramic technology, the latter of which has been a standard in clinical dentistry for more than thirty years, has entailed a number of exacting steps to create the ultimate restoration. These steps are generally as follows:
1) Tooth preparation. Removal of 1.5 to 2 mm. of tooth structure, i.e., enamel or dentin to provide a preparation of the tooth without undercuts and to allow a final metal ceramic or metal resin restoration that is of adequate thickness.
2) Impression (negative mold): Use of an impression material such as a hydrocolloid, polyester rubber, or vinyl polysilicone (VPS) to make impression of tooth preparation.
3) The impression is then used by the laboratory technician to create a stone or epoxy model with removable dies that are an accurate copy of the prepared tooth, i.e., to create a positive replication of the tooth.
4) Painting of a die spacer onto the die, which affords appropriate relief in a range of 20 to 36 microns to allow space for a dental cement or bonding agent to secure the final restoration to the patient's prepared tooth.
5) A lubricant or a release agent is then placed over the die spacer.
6) A wax pattern is then fabricated over the lubricated die.
7) The wax pattern is then invested in high heat investment material and cast from a molten metal using the "lost wax" technique and a centrifuge process to form a metal coping or substructure of the restoration.
8) The ceramic or visible portion of the restoration is then formed by applying and baking successive layers of porcelain powders mixed with distilled water or other types of porcelain building-up liquids, first to opaque over the metal coping to hide the metal color and then to shape the porcelain from its various transition shades to create as natural an appearance as possible. The temperatures of this baking is a function of individual vendor's particular protocol.
Recent technologies now provide systems in which a metal substrate or substructure is no longer required. Therein, the restoration is fabricated using pressable ceramic that can be made and processed by use of lost wax technology to create ceramic substructures. Such ceramic substructures formed therefore require the fabrication of a second shading die. This die is fabricated from a light cured resin stump of the pressable ceramics. It is fabricated by packing this stump material into the ceramic substrate which first coated with a liquid separator, and inserting a plastic holding rod into the resin stump material. The technician cures the material by holding it under a curing light for approximately 1-2 minutes per die. After curing, the remain stump die is removed, a wetting agent is placed over the die, and the die is then put back into the ceramic substrate allowing the technician to do the coloration. The wetting agent permits the transmission of color of the stump material through the substrate. This process includes costly materials and is most time consuming for the technician as compared to the instant invention.
In the invention, for the technician to correctly complete the extrinsic color shading technique on the original die, a die spacer color, matched to the intrinsic stump guide, is needed. This die spacer is opaque and masks out any shade of the die stone used to fabricate the die replacing it with the correct dentin or intrinsic shade. Due to such use of the die spacer, the dental ceramic substructure will have the proper relief for the bonding resin when the restoration is placed on the tooth preparation of the patient. This die spacer is used both to wax up over to create the spacer for the cement as well as for finalizing the extrinsic shades. Thereby only one die preparation is needed.
One of the most exacting and time consuming aspects in the making of a pressed porcelain restoration is that of properly matching the color of the restoration to that of the natural tooth of the patient. Color, in the context of clinical dentistry, has evolved as a complex combination of art and science in which color is differentiated into discreet concepts of hue, value, and chroma. Therein, hue is defined as the dimension of color that enables one to distinguish one family of color from another. Value is defined as the parameter of color that permits one to describe the relative whiteness or blackness thereof, while chroma, as the third dimension of color, defines the relative concentration, strength, saturation or intensity of hue. That is, the more intense a color is, the higher is its chroma level.
These qualities follow the Munsell color system for designating color which employs three perceptually uniform scales (Munsell hue, Munsell value and Munsell chromo) defined in terms of daylight reflection. (McGraw-Hill Dictionary of Scientific and Technical Terms--3rd Ed.). Translucency or the quality of transmitting and diffusing light, provides a perception of depth that is also an important parameter.
The art of coloration of new ceramic/porcelain restorations has been substantially the same as that of traditional metal-ceramic technology. That is, such prior art has related to a variety of techniques of surface treatment including techniques of staining, glazing, and polishing to attempt to correct the hue, chroma, or value of a restoration to that of the natural tooth of the patient. In this process, the starting point has always been that of opaquing the bottom surface of the restoration. However, in the new, all-porcelain and/or pressable ceramic techniques (as applicable to the crowns, onlays, inlays, veneers and bridges), the color of the above-referenced die spacer is of enhanced importance because, unlike metal-to-ceramic technology, there does not exist a metallic or opaque substructure to the pressable ceramic restoration. Accordingly, the effect of the die spacer on the color of a pressable ceramic restoration is most influential in the process of coloration of the pressable ceramic cast restoration.
In the prior art, the role of the die spacer has never been that of matching, or attempting to match, the hue, value or chroma of a tooth preparation or dentin shade, this as noted above, because the dental metal substructure of traditional metal-to-ceramic technology created an opaque inner coping to the restoration. Therefore, the die spacer was never visible. Die spacers have been designated to match the shading of opaque cement. But these opaque cements prevented the need to have die spacers to match the dentin shades. For example, U.S. Pat. No. 4,650,418 (1987) to Blair, held by Dentsply, which teaches the DICOR method, employs internal coloration of a dental cement to modify or correct external of duplicating the shading of the opaque cement which was color coordinated to the extrinsic shade of the shade guide.
Dental die spacers used in the present system (the instant invention) do not attempt to match a dental cement, but rather match the shading of the dentin of the patient's tooth stump, while using a clear resin cement. Therefore, the instant system uses an entirely different basis of coloration.
The instant invention addresses the new requirements and opportunities of color science in clinical dentistry associated with the all porcelain and pressable ceramic (or other clear material) restorations resultant from the fact that such new systems do not utilize a substrate which is inherently opaque.